The present invention relates to injection molding machines, and in particular to valve gate systems for injection molding machines, and injection molding machines having molds using valve-gate systems for controlling the injection of molten plastic into the mold chamber.
Valve-gate systems have the advantage of creating a clean, flush gate mark, when minimal vestige height is required on the molded part. Apart from a cosmetic viewpoint, larger orifices allowed by valve gates prevent drooling, reduce shear heat and molded-in stress, provide easier filing and reduce injection pressure. Valve-gates are typically part of a larger unit (commonly referred to as “valve-gate unit”) that is mounted behind the gate area, in firm contact with the hot runner's manifold. More issues regarding existing valve-gate unit designs are raised below.
While existing valve gate systems create quality gates on molded parts, they also suffer from certain shortcomings, as described below.                The valve pin or stem of a valve gate unit is actuated typically by pneumatic or hydraulic systems, included in the body of the valve-gate unit, which contributes to increase valve pin length.        Pneumatic or hydraulic actuating systems included in heated valve-gate units are continuously subjected to high temperatures, and therefore likely to suffer from problems associated with thermal expansion.        Pneumatic or hydraulic actuating systems mounted behind the manifold require cooling. If no cooling is available, they generally will require regular maintenance checks (e.g., to inspect and/or change o-rings, etc.), which adds to the overall cost of the operation of the machine.        Presence of pneumatic or hydraulic systems in valve-gate units may limit the use of back-to-back gating for stack molds. In such cases, when using a single manifold, staggered placement of gates may be required, resulting in increased projected area. It is noted that back-to-back mounting can be achieved if using multiple manifolds, but, in such cases, equalizing flow in all runners (e.g., to avoid preferential flow) becomes an issue.        Many of the existing valve-gate systems have no form of adjustment of the valve pin length. An adjustment of some sort is typically necessary to bring the valve pin flush with surrounding molding surface. Existing systems that have this adjustment still require a fair amount of work, even with the mold in the injection press, resulting in increased downtime.        
There is therefore a need for an improved valve-gate unit that does not suffer from these issues.